1. Field of the Invention
The present invention relates to an antenna architecture for non-interacting connection of an antenna to a power amplifier, the antenna being connected to the power amplifier via an LC coupler, as well as an LC coupler.
2. Description of the Related Art
In a modern wireless communication system, such as the mobile wireless standard UMTS or in a wirelessly networked computer network, a so-called wireless local area network (WLAN), the digital data to be transmitted is transmitted via a wireless connection in the gigahertz range. For example, in the UMTS standard, frequencies between 1,900 and 2,170 GHz are used and frequencies around 2.4 GHz are used for a WLAN. For wireless signals of these frequencies, the wavelengths are a few centimeters and thus in the microwave range. Wireless signals of this wavelength may thus be interfered with by comparatively small objects, the interference effect of an object being a function of the distance of the object to the antenna and the electrical conductivity of the object. The lower the distance of the object to the antenna and the greater its electrical conductivity, the stronger the interference with the wireless signal transmitted by the antenna. The interference may cause the propagation of the wireless signal to be impaired, in addition, the wireless signal may be deflected in its direction, in particular reflected, so that the reflected component is guided back to the antenna, for example.
If necessary, and particularly in the case in which an object having good electrical conductivity is in proximity to the antenna, not only does an object interfere with the propagation of the emitted signals, but rather, for example, due to the small distance, changes of the antenna characteristic also result, in particular of the input resistance of the antenna.
In practice, the antennas of such a UMTS or WLAN device are connected nearly directly to a power amplifier, so that the resistors must be adapted for optimum transmission of the transmission power between the power amplifier and the antenna. In the ideal state, i.e., if no interfering object in proximity to the antenna changes the antenna characteristic, adaptation is provided. However, if the input resistance of the antenna changes, this results in a change of the operating point of the power amplifier and the transmission behavior. In practice, the value of the error vector magnitude (EVM value) rises, which is used as a measure of the linearity deviation of high-frequency power amplifiers.
However, to achieve a high data transmission rate, linear transmission behavior of the upstream power amplifier must be achieved. A shift of the operating point of the power amplifier, which is accompanied by a rising EVM value, is thus disadvantageous. Attempts to design a power amplifier as so robust in its behavior that a proximal object having good electrical conduction does not influence the operating point have remained unsuccessful until now.
It is known from the prior art that in such systems so-called “isolators” are used, which are connected between the antenna and the power amplifier and “isolate” the power amplifier from the antenna to thus prevent feedback on the power amplifier. These isolators thus cause the operating point of the power amplifier not to be shifted from the ideal point. Furthermore, in addition to these isolators, which comprise passive elements, work has also been done on electronic regulating solutions, in which electronic regulators are used. Such isolators and electronic regulating solutions are described, for example, in Bezooijen A., Chanlo Ch., Roermund A. H. M., Adaptively Preserving Power Amplifier Linearity under Antenna Mismatch, IMS2004, Fort Worth.
The use of such isolators known from the prior art has multiple disadvantages. Isolators are costly, they require a large amount of space, and they have a high weight in comparison to other components. Furthermore, they have a high damping, so that the output power output by the power amplifier is not transmitted optimally to the antenna and thus emitted. This results in an increased power consumption by the amplifier and therefore, in particular in battery operated mobile wireless devices, such as UMTS mobile telephones, so-called handsets, result in the batteries draining rapidly. Furthermore, the isolators based on electronic regulation may tend toward instability because of the feedback control circuit, which possibly causes further undesired interference. The use of isolators of this type for decoupling the antenna from the power amplifier is thus possible, but connected with great disadvantages and difficulties.